Typically, the optical systems used in the context of fabricating microelectronic devices such as semiconductor devices include a plurality of optical element modules including optical elements, such as lenses, mirrors, gratings etc., in the light path of the optical system. Those optical elements usually cooperate in an exposure process to illuminate a pattern formed on a mask, reticle or the like and to transfer an image of this pattern onto a substrate such as a wafer. The optical elements are usually combined in one or more functionally distinct optical element groups that may be held within distinct optical element module groups.
With such optical systems, typically, such optical element module groups are often built from a stack of optical element modules holding one or more—typically but not necessarily rotationally symmetric—optical elements. These optical element modules usually include an external generally ring shaped support structure supporting one or more optical element holders each, in turn, holding one or more optical elements.
Due to the ongoing miniaturization of semiconductor devices there is a desire for enhanced resolution of the optical systems used for fabricating those semiconductor devices. This desire for enhanced resolution obviously pushes the desire for an increased imaging accuracy of the optical system. Furthermore, to reliably obtain high-quality semiconductor devices it is not only desirable to provide an optical system showing a high degree of imaging accuracy. It is also desirable to maintain such a high degree of accuracy throughout the entire exposure process and over the lifetime of the system. As a consequence, the components of the optical system cooperating in the exposure process desirably are supported in a defined manner in order to provide and maintain a predetermined spatial relationship between the optical system components which, in turn, guarantees a high quality exposure process.
In order to reduce imaging errors that may arise during operation of the optical system, it is known to actively control the position of one or more of the optical elements of the optical system. Such an optical system is known, for example, from U.S. Pat. No. 5,822,133 (Mizuno et al.), the entire disclosure of which is incorporated herein by reference.
It is also proposed to actively deform some of the optical elements, i.e. actively control the geometry of some of the optical elements.
A special focus may be put on the design of the contact elements of the support structure contacting the optical element or an eventual holder holding the optical element (in an optical element unit including the optical element and such a holder).
A typical support structure for an optical element used in the context of such optical systems is known, for example, from U.S. Pat. No. 7,154,684 B2 (Shibazaki), the entire disclosure of which is incorporated herein by reference.